1. Field of the Invention
This invention relates to devices and processes for metal organic chemical vapor deposition. More particularly, this invention pertains to a apparatus and methods for creating a generally flat temperature zone on a substrate for growing semiconductors.
2. Description of the Prior Art
In the past, chemical vapor deposition on substrates which achieved satisfactory yields has generally required devices of high energy consumption. Typically, a wafer of gallium arsenide is heated prior to and during vapor deposition through a system utilizing electromagnetic radiation or radio frequency induction heating. The costs of this equipment for generating heating for wafer deposition is high and the costs of operating is expensive as a result of high energy consumption and the inability to efficiently utilize and direct energy.
A system has been tried using a carbon block used as an electrical resistance heating element beneath a quartz support. One difficulty encountered with carbon block resistance heating is that there is a lack of uniformity in heating of the water, resulting in lower quality yields.
A low pressure MOCVD system has used a reactor having a hexagonal SiC coated graphite sample holder which is heated by quartz halogen lamps placed at its center. The lamps are enclosed in a double quartz walled jacket which isolates them from the sample holder. The walls of the substrate holder are slightly tilted backward toward the center of the holder and each face has recesses for 3 inch square wafers. A total of 30 to 50 wafers can be processed in a single run. Power to the lamps is controlled by a computer which monitors and controls power to maintain it at a constant level. An operator can observe temperature through a small "peephole" in the reactor chamber but there is no feedback temperature control. Temperature variations in this system are large and uncontrollable. The major disadvantage of this system is its high initial and process costs.